include special period 13 data on copy of Report RFBILA00 when retrieving data posted for period 12

Hi Experts.

I am working on a copy of the standard report RFBILA00 which was made by another company, my requirement is to change the report, so it can also show data for special period 13 when data for period 12 is retrieved.

This report has no selections for period (select options BILAVMON),it was probably removed by another developer.

When we select data using the last date of period 12 ( pa_date screen field = 31.12.2018), the report has to include data for period 13 as well.

I know that the report uses SDF logical database, but I am new to logical databases. Can you tell me where I can make changes to achieve what is needed.

Every contribution is welcome.

Thanks in advance.